The present invention generally relates to fluid seals and more particularly to the sealing of rotary shafts wherein both dynamic and static seals are utilized. The invention is uniquely applicable to the sealing of propeller shafts that are located underwater for driving both underwater and surface vessels.
Many prior art devices for providing sealing systems are readily available. For providing static seals, O-rings are commonly used. For rotary dynamic seals two smooth plates can be utilized with pressure exerted on one of both of the plates to hold them in equilibrium with each other. A fluid film normally forms between the mating pieces. A plurality of systems for providing a force to hold the mating pieces in equilibrium with each other have been developed. Among these are a simple spring or bellows arrangement in which one of the plates has axial movement. In such a system the spring or bellows is placed on the end of one of the plates that has slight axial movement in relation to the other plate. The end of the plate chosen is the one away from the mating plate so that the spring exerts a force holding the two plates in abutment.
Another known system uses fluid pressures that tend to equalize on the front and back sides of the movable seal plate. However, the back side of the movable seal plate has a larger area thereby increasing the force to keep the seal plate tight against its mating component.
Such devices, although useful, cannot have the force varied to a desired amount should outside pressures increase such as when a submarine submerges to a lower depth. They are also incapable of being varied as slight differences in optimum closing force occur over extended periods of time as slight wear occurs on mating surfaces. Other influences on optimum closing force include viscosity, density, ambient pressure, speed, temperature, etc. Variable pressure systems have been developed but are for the most part complex with flowing fluid necessary in the operation of such devices.